Alterations in Gill Epithelial Morphology of Yearling Sunapee Trout Exposed to Acute Acid Stress

Scanning electron microscopy was used to examine gill filaments of hatchery-reared yearling Sunapee trout Salvelinus alpinus oquassa that had been exposed to acute acid stress in static-water bioassays. Fish exposed to acidified water at pH levels above those that caused acute mortality showed little alteration in gill morphology. Exposure to acutely lethal levels of acidity caused considerable damage to gill epithelia, including primary lamellar swelling, increasingly rugose secondary lamellar surfaces, increased mucus production, and fusion of adjacent secondary lamellae. Additionally, the loss of microridge patterns on the epithelia of the secondary lamellae became more severe with decreasing pH. Such alterations may decrease the surface area available for gas exchange and contribute to the anoxia that appears to be an important source of mortality at very low pH. Received November 18, 1982 Accepted June 4, 1983